Automatic telephone system



Dec. 29, 1925.

E. E. HINRICHSEN AUTOMATIC TELEPHONE SYSTEM Filed March 30, 1922 5 sh t -Sheet 1 /n vemar: faWa/"c/ f. H/hr/chsen.

Dec, 29 1925 Y E. E. HINRlCHSEN AUTOMATIC TELEPHONE SYSTEM Filed March 30, 1 5 Sheets-Sheet 2 //7 van for: Edward E. fi/hrfchsen.

Affy.

Dec. 29,1925. 1,567,054

E. E. HINRICHSEN AUTOMATIC TELEPHONE SYSTEM Filed March 50, 1 5 Sheets-Sheet 3 b W A/y y AUTOMATI C TELEPHONE SYSTEM Filed Mrch 30, 1922 5 sheets-Sheet 4 me Q \Q w? w v N //7venf0r: fdward t. H/hn'chsen.

Dec. 29, 1925: 1,567,054

E HINRlCHSEN AUTOMATI C TELEPHONE SYSTEM Filed March 30, 1 5 Sheets-Sheet 5 //1 venfor: Edward L fflhr/chsen.

Patented Dec. 29, 1925.

STATES;

1,567,054 PATENT OFFICE,

EDWARD E. HINRICHSEN, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE SYSTEM.

Application filed March 30, 1922. Serial No. 548,078.

To all whom it may concern Be it known that I, EDWARD E. I-IINRICH- sen a citizen of the United States, residing at. New York, in the county of New York,

State of New York, have invented certain new and. useful Improvements in Automatic Telephon .v Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems and particularly to subscriber-operated switching means for private branch exchange working.

Its object is to provide a system of this type which shall be simple and efficient in operation and cheap to manufacture.

It is an improvement upon the system disclosed in my application'Serial No. 396,143, filed July 14, 1920, Patent No. 1,507,116,. granted September 2, 1924.

One of the features of this invention is the provision of means for registering the first selecting impulse by apparatus individual to the link circuit and in the course of this registration connecting the link circult to common apparatus adapted to register the second and subsequent impulses.

A further: feature: is the provision of a circuit arrangement for preventing the careless removal ofthe receiver by the called partyjrom falsely causing the operation of. a recall signal at the operators position. In recall circuits heretofore known,.theresponse of the called subscriber immediately prepared a recall circuit which was closed upon a subsequent break in the line circuit caused by the subscriber in depressing his switch hook to notify the operator that he desired to make another call. This. recall circuit-1mcluded. a signal which remained displayed before the operator, thus relieving the: subscriber of having to. move his receiver switch hook up and down until the operator answered. In accordance with this invention, means is provided to interpose an interval of time between the raising of the switch hook in response to the call and the preparing ofthe recall circuit. Thus a fluttering of the switch hook contacts will not, by again immediately opening the line after it has once been closed, cause the false display of the re call signal.

More specifically the circuit of the recall signal includes a normal. contact of a relay which is locked up at the time the called subscriber answers by a circuit independent of the called supervisory relay. The response of the called party operates a timing device which only after an interval transfers the'control of the said locking circuit to the front contact of said supervisory relay, so that any deenergizations of said relay during said interval cannot release saidlockingrelay because it is held operated in acircuit independently thereof, but a. deenergi-zation of said relay after said interval releases said locking relay to close the recall circuit.

Another feature is the provision of a circuit arrangement for economizingcurren'u which is desirable in small private branch exchanges such as the one disclosed herein. This feature contemplates providing a link circuit which maintains the talking circuit between two'stations closed by means of only two energized relays, one of which connects the calling station to the. link circuit and the other of which. connects the called station: to: said link circuit, a relay being provided in the link circuit for controlling the ringing of the called. line, the talking circuit including normal contacts of said relay.

Still another feature is the use of the ringing trip relay as abusy test relay.

These and other features of the invention will be-more particularly described in the following detail description.

The drawin s when placed with Fig. 2 to the right of Fig. 1, Fig. 3 under Fig, 1, Fig. l tothe right of Fig. 3, and Fig. 5 under F ig 4, diagrammatically illustrate a telephone system embodying the invention Figs. 1 and 2 show a part of the line and the trunk circuits. Figs. 3 and 4 show the remainder of the line circuits and the link circuits. Fig. 5. shows the counting relay, ringing and tone circuits.

Subsom'bcrs Zine circuit.

The station line circuit, for example, of line No. 1, comprises the line relay 300 and the cut-off relay 301. \Vhen the station originates: a call, relay 300 operates and causes the operation in the first idle link circuit of the finder relay 302 corresponding to the calling line, and also operates the holding relay 309 of the link circuit. As soon as the line is connected to the link circuit, cut-off relay 301 operates and cuts oil and releases relay 30-5). When a station is called, relay 301 is operated to cut off relay 800 and prevent it "from operating when the subscriber answers. When the link circuit is released, at the end of connection, relay 801 releases and the line is ready for another call.

Goa-Ming relay circuit.

The counting relay circuit, shown in the upper part of Fig. 5 is common to all the link circuits, but is not used in connection with the trunk circuits. It is so arranged that it is not attached to a link circuit until the subscriber connected with that circuit actually operates his dial. The first impulse of a selection is used up in the link circuit in attaching it to the counting relay circuit, but the second and subsequent impulses are recorded in the counting relay circuit.

-VVhen a link circuit picks up the counting relay circuit, relay 500 operates, cutting the dial tone off from all the link circuits and preventing any link circuit other than the one which is connected, from responding effectively to impulses from the subscribers calling'dial. The operation of relay 500 also supplies battery to the relays 501, 502, etc. The second selecting impulse from the link circuit operates relay 501 which locks up through the left-hand winding of relay 502. This relay, however, is short-circuited until the removal of ground from the winding oi relay 501. Assoon as this takes place, 502

operates through its left-hand winding and locks up through both windings in series, releasing 501 and connecting the'locking circuitof 501 to the third counting relay which is not shown in the drawing, but is connected in thesame manner as shown for the ninth relay503.

- If only one selecting impulse is sent, none of the counting relays 501, 502, etc. are operated and ground is supplied through the back contacts of these relays in series for operating the'firstconnector relay- 303 of the link which connects station No. 1' to the link. The particular connector relay -C which operates at the end of the selection is determined by the number oif'counting relays which have been operated.

Ringing circuit. I V

' The ringing circuit shown .in the lower part of Fig. 5 is common to all the links and trunks, and is arranged to convert direct current from the private branch exchange battery into interrupted alternating current for ringing the bells at the stations. VVhenever any link circuit or trunk circuit-is in the ringing condition, relay 505 operates, operating'relay 506. Relay 506 locksup and operates 507. Relay 50?, when it operates, locks up and short circuits and releases relay 506. The release of relay 50s short-circuits and releases relay 507. Relay 50 now operates again, andethis cycle of operation is continued as long as relay 505 relay 508, which in turn operates relay 509.

Relay 509 cuts OH and releases relay 508. This releases relay 509 and permits relay 508 to operate again. These relays are sluggish so that their continued operation and release supplies ground intermittently to relays 510 and 511. The first operation of relay 509 operates relay 510, and when relay 509 releases relay 510 remains operated in series with the left-hand winding of relay 511, which operates and removes a shortcircuit from its right-hand winding, and supplies battery to the primary windings of the ringing transformer.

On the next operation of relay 509, relay 510 is short-circuited and released, cutting off battery from the transformer primary, but relay 511 is held operated until relay 509 releases again. This cycle of operations continues as long as relay 505 remains operated, andas relays 506 and 507 are going through their cycle continuously, alter nating current will be induced in the secondary of the ringing transformer whenever battery is supplied to the primary by the action of relays 510 and 511.

The secondary winding of the transformer is grounded through the battery in order to supply superimposed current during the silent interval for operating the tripping relays. Tone and buzzwcircm'ts. The tone circuit, shown at the lower lefthand corner of Fig. 5 supplies dial tone and busy tone to the link circuits and busy tone to the trunk circuits as required. Relay 512 is operated whenevera link circuit is in useor 'when the attendant is making a selection by means of a trunk circuit. This causes relay 518 toope'rate as a buzzer and supply a suitable tone.

The buzzer relay 100 at the attendants station, Fig; 1, is in series with the battery supply to the line lamps 200 alsoat the attendantsstation, these lamps being individual to the trunks. On an incoming call the lamp 200 of the trunk seized is lighted and the buzzer relay 100 is also operated.

By operating the key 101 the attendant may silence the buzzer without extinguishing the line lamp 200.

Selecting key circuit.

The selecting key circuit shown at the top of Fig. 1 is common to all the trunks.

lVhen any of the selecting keys is depressed,

relay 10;? operates, operating relay 103, and supplying ground for operatlng the testing relays in the trunk circuit; at the same time another contact of the key closes a circuit through contacts of a relay in the trunk circuit to the proper trunk connector relay TC to connect the trunk to the desired station. Relay 103, when it operates, locks up, and cuts off and releases 102.

Attenalcm ts telephone circuit.

The attendants telephone circuit, Fig. 1, consists of a subscribers set like those used at the other stations. It may be connected to anytrunk circuit by means of a trunk circuit listening key 201. An additional key 104 is provided for connecting the set to the attendants station line conductors. The key has a holding position in which a resistance 105 is bridged across the line circuit, so that the attendant may hold the line in case she has occasion to answer a call on a trunk circuit at a time when she is talking on a local connection.

Link circuit.

The link circuit shown on Figs. 3 and 4 may best be described by setting forth the operations involved in establishing a connection from one subscribers station to another.

. lVhen the subscriber at substation No. 1 originates a call, the line relay 300 is operated by a circuit including the substation set (not shown) of line No. 1, and operates slow relay 309 over a circuit including the following elements: ground, 304, 305, 306, 307, 315, 308, 309 to battery. It is assumed that the lower link circuit was in use when this call originated and, therefore, relay 310 of this link circuit is operated to advance the starter wire 306 to the next idle link, shown as the upper link. By the operation of the line relay 300, a. relay 302 corresponding to-the calling line No. 1 is operated to connect the :alling line to the link circuit used.- This circuit includes the following elements: ground, 311, 312, 302, 313, 314, 315, 316, to battery. Relay 302 operates through its left winding and locks through its rightwinding to ground supplied by relay 309 and connects the calling line to the link, Belay 302 in attracting its outermost right armature operates the cutoff relay 301 of the calling line.

Impulse relay 400, Fig. 4, now operates through the telephone set of the calling line and operates relay 317. This circuit in eludes the following elements: battery, left winding of 317, sis, 330, 4.01, 402, 403, 527, 512 to ground. Relay 317, on operating, supplies ground through a contact of relay 309 and its own right winding and the winding of relay 319 to battery, operating relay 319. The operation of relay 319 cuts off battery on the conductor 315 from the left windings of all the relays F of the link circuit used and supplies it to the next link circuit, and places a relay corresponding to 309 of such link circuit under control of the line relays L.

Relay 400, Fig. 4, now controls slow relay 309 througli the left contact of relay 317, and the right armature of relay 317 closes a circuit for stepping relay 404. This circuit includes the following elements:battery,405, 404, c, 10?, 408,409, 341, 34-0 to ground. But relay 404 is short circuited at this time by the outer contact of relay 400 so that it does not operate.

When the subscriber at station 1 actuates his calling dial (not shown) to select any desired station, relay 400 releases at each interruption of the linecircuitby the dial springs, removing the short circuit from about relay 404, and permitting it to operate in the circuit traced. The first operation of relay 404 operates slow relay 410, this circuit including the inner armature and normal contact of relay 411 and the inner armature and alternate contact of relay 404. If the counting relay circuit shown on Fig. 5 is not busy, slow relay 419. now operates in a circuit including the outer armature and alternate contact of relay 404 and the right armature and normal contact of relay 500, Fig. If the counting relay circuit which is common to the link circuits is busy at this time, slow relay 500 is energized and relay 412 cannot operate. If the counting relay circuit is not busy, relay 412 operates and its right armature supplies its winding with battery independently of the original energizing circuit for this relay, and in attracting its left armature, this relay closes a circuit for relay 411 through the winding of relay 410, but relay 411 is short circuited at the inner armature and alternate contact of relay 404 and therefore does not operate until relay 404 releases. On the release of relay 404 by the dial at the end of the first impulse, relay 411 operates and places the counting relays under the control of stepping relay 404. Relay 410 supplies a groundtothe counting relay circuit to operate relay 500 to make the counting relay circuit busy to other links. When relay 404 releases as the dial reaches normal, relay 412 which is sluggish enough to hold up through the selection, releases and opens the circuit of relay 410. Relay 410, however, also slow in releasing and a circuit is closed from the left grounded normal contact of relay 412 through the outer armature and alternate contact of relay 411 through the right contact of relay 410 which operates relay 413- and holds relay 411 operated by its left winding. On the release of relay 410, relays 411 and 413 release and relay 500 releases and the counting relay circuit is, by the release of this latter relay, made a 'ailable for other calls.

Relay 413 in operating supplies ground from the counting relay circuit to that one of the relays C of the connector correspond ing to the called line. The counting relay circuit shown in Fig. 5 is common to all the link circuits. It is so arranged that it is not connected to a link circuit until the sub-- scriber connected with that circuit actually operates his dial. The first impulse of a selection is used up in the link circuit in connecting it to the counting relay circuit but the second and subsequent impulses are re corded in the counting relay circuit. Relay 500, Fig. 5, in its normal position, supplies battery for the operation of relay 412 in the link circuit as described. Relay 500, at its left armature 'andnormal contact, supplies dial tone to the link circuit used and thence to the calling line to inform the calling subscriberthat the circuit is in condition to receive the impulses. The circuit for applying this tone to the link used includes the following elements: 515, 516, 517, 415, 416, 417, 418, 419, through the lower link conductor 446 and the substation, returning over the upper link conductor 447 to ground through the left winding of relay 400. When a link circuit picks up the counting relay circuit, relay 500 operates, disconnecting the dial tone from the link circuits whereby a calling subscriber knows that the common counting relay circuit is in use, and preventing any link circuit other than the one which is connected from responding effectively to impulses from the subscribers dial. Relay 500, at its right armature and alternate contact supplies battery to the counting relays 501, 502, etc.

The second selecting break in the line circuit by the dial operates relay 501, this circuit including the inner armature and alter nate contact of relay 404, inner armature and alternate contact of relay 411, 419, 420, 518, 501, 519, right armature and alternate con tact of relay 500 to battery. Relay 501 locks up through the left-hand winding of relay 502, which is, however, short circuited until 7 the retraction of the inner armature of relay 404 at the termination of the second impulse. When this takes place, relay 502 operates through its left winding and locks up through both windings in series, releasing relay- 501 and connecting the locking circuit of relay 50-1 to the third counting relay which is not shown on the drawing, but is connected in the same manner as shown for relay 503.

If the digit dialed is 1, none of the counting relays are operated and ground is supplied through the left-hand back contacts of the counting relays in series for operating the first connector relay C of the link. The connector relay C which operates at the end of the selection is determined by the number of counting relays which have been operated. In assuming that two impulses have been transmitted to select station No. 2 shown in Fig. 1, relay 413 in operating, supplied ground over the left normal contacts of counting relays 504, 503, etc., left alternate contact of relay 502, 520, 421, 422, 423, 321, 322 to battery. Upon the release of slow relay 410, relays 411 and 413 release and relay 500 releases whereby the counting relay circuit is made available for other calls. Relay 500 in retracting its left armature again connects dial tone current to the link circuits. Relay 322 looks up to ground on conductor 320 and connects line No. 2 to the used link. Relays 424 and 425 are also operated by the operation of relay 413. Relay 425 cuts off the called line and connects it through the normal contacts of relay 424 to the ringing circuit shown in Fig. 5, but as relay 424 is operated, ringing circuit is not yet applied to the called line. Relay 425 locks up in a circuit including the following elements: battery, starting relay 505 of the ringing circuit (Fig. 5) 521, 426, 427, 425, 428, 409, 320 to grounded conductor 340. Relay 424 in operating, con-' nects the sleeve conductor 437 by way ofa normal contact 430 of relay 429 to the left winding of relay 431 to test for the idle or busy condition of the called line. In case the line is busy, its sleeve 326 is grounded as will hereinafter appear so relay 431 operates. Relay 431, in operating, opens the locking circuit of relay 425 and operates relay 429 from ground on conductor 409. Relay 429 at its inner left armature supplies ground for locking up relays 424, 425

and 431, these circuits including the left armature of relay 424. Busy tone issupplied to the calling line by the operation of relay 431. This circuit leads from conductor 515, 522, 432, 433, 418, 419, and over the circuit traced for the dial tone to ground through relay 400. The circuit remains in this condition until the calling subscriber restores his receiver.

In case the called line is not busy, its sleeve conductor 326 is not grounded and relay 431' does not operate upon the operation of relay 424. Relay 424, therefore, re leases upon the release of relay 413 and connects the sleeve 3260f the called line through the left winding of relay 460 to ground, whereupon relay 460 operates in series with the cut-off relay 324 of the called p This circuit includes the follow- 111g elements ground, 460, upper link con line No. 2.

ductor-.434, 435, 430, 436, 437, 323, 325, 326, 324 to battery. Relay 460 operates relay 429 which looks up to grounded conductor 409. Relay 429 in attracting its inner left armature, places a direct ground upon the sleeveplies interrupted ringing current through the right winding of the relay 431 to the called from the ringing circuit shown Fig. 5, apart of the ringing current passing through condenser 419-tothe calling line giving the calling subscriber an indication that ringing is going on. The circuit for signalingithe called subscriber includes the tollowingelements: battery, secondary of the trailsfornier 52.3., 524, 437, 438, 431, 439, 440, lower link conductor, through the bell 135 at. the called station No. 2 returning over; the upper link conductor, 461, 441, 442., 443,, 525,. :to ground. The circuit .over which ringing tone is transmitted to the calling party No. 1. leads from 444, 445, 417, 418, 419, 449;, 446, through the calling substation, returningover link conductor 447 to ground tlnough relay 400.

In response to the ringing of the bell 135, the attendant operates key 104 and removes the receiver, whereupon relay 431v operates through its right winding, and in attracting its outer left armature releases relay 425 whidh connects the called line through condensers 448., 449 to the calling line. Relay 431 releases upon the release of relay 425. Tal'kiing' currentfor the called line is supplied through relay 460 which operates.

When the calling subscriber: restores his receiver, relay 400 releases, releasing relays 309 and 512. This releases relay 302 and restores the calling line to normal. If the called party has also hung up his receiver, the release of relay 309 releases relays 317, 319, 429 and 322, and thelink circuit is ready tor another call. If, however, the called party lias not restored his receiver, relay 400 remains operated and prevents the release of relay 429, and ground through the; contacts of relays 460 and 429 holds up relays 3117., 319 and 322, and prevents the release" of. the link circuit until relay 460 releases.

Trim]: circuit-originating calls.

.118112 subscriber say at station No. 1 dlalsztlredigit 0., to select-a trunk to the central oflice, relay 41.3 is operated at the end of selection, as describedin connection with a local call,.;and operates relay 327 in place of-Qne the relays IC. Relay 327 in attractinigtits leitt armature grounds lead Ofthc calling line over 334 due to the energized condition of relay 302. In closing itsinner right contactrela-y- 327, looks to ground the. armature or slow relay 309 and at its-outer right armatureflextends the grounded conductor 401 to conductor 331 aIldit-hQnQQ to relay 107, Fig. 1, and slow holding relay .1202, Fig; '2. The circuit for relay 107 leads from grounded [conductor 40.1, 330,331, 108, 109,-:(relay' 110 being operated since the: lower :trunk is assumed to be busy) 111, 107to battery. The circuit for relay 202 leads from conductor 109, 112, 118,203, 202 tobattery. Relay 107 connects leadsLof all lines. to the corresponding relays TC, and the proper relay, in this case 113, operates to connect the calling line to the trunk circuit. The circuit tor relay 113 is as follows: battery, 113, 115, L lead 116, 114,332, 333, 334, to ground at the left armatureof relay 327. Relay 113 looks up to ground at an alternate con-tact of the holding relay .202. This circuit is as follows: 113, 136 204, 205, 206, 207, 208, to ground at the right armature and alternate contact of holding relay 202. Relay 202 also lights the busy lamp 210 and closes a circuit including relay 117. Relay 117, however, does not operate at once as it is shortcircuited by the ground supplied over conductors 108, 109 from the link circuit. As soon as the link circuit releases .due to the release of slow holding relay 309, the circuit of which was opened at contact 318 when relay 327 operated, it removes the short circuit from relay 117 which operates. Relay 211 now operates over the trunk circuit and calling subscribers line loop. The operation of relay 117 releases relay 107 and puts slow relay 202 under control of relay 211, so that relay 202 isnow held operated over the following circuit: battery 202, 203, 118, 119, 212, 213, 453, 527, 512 to ground. The operation of relay 117 also places relays corresponding to 107 and 202 of the next idle trunk under control of the link circuits. As soon as ground is removed from the sleeve lead 122 of the calling line by the release of relay 302 which releases when holding relay 309 of the link circuit releases due to relay 327 operating relay 214 operates in series with out-oft relay 301 of the calling line. This circuit is as follows: ground, 214, 215, 218, 216,217, 120, 122, 335, 301 to battery. Relay 214, in operating, energizes relay 219 as follows: battery, 219, 220, 221, 205 to ground at the right alternate contact of slow holding relay 202 over the path previously traced. Relay 219 in attracting its inner lelt armature short circuits relay 214 and in attracting its right armature locks to groimded conductor 205..

Current is supplied to the telephone set of the calling subscriber through relay 211, which grounds the tip side of the line to the central .oifice through normal contacts of relays 224 and 225, and the listening key 201. The circuit of the central olfice is arranged with its tip connected to battery through the relay 290, so that the opera- 'tion: or" relay211 operates the line relay at the central office which lights the line lamp 29 dis-soon as :the operator answers by inserting, a plug (uotshown) in the jack298, the leads 220,227 are connected to ground and battery. respectively, throng-lithe plug and relay 228 operates, operating slowholding relay229. The circuit of relay 228, leads from the upper ortip conductor 226, 231, 228,260, 233, 252, 234, 235,236, to the lower or ring conductor 227. The operation of relay 229 closes a circuit through relay 230, which operates and connects the calling line through to the central office. The circuit for relay 230 is as follows: Left armature and alternate contact of relay 229, 237, 248, 252, 238, 239, 230, 240, 241 to battery at an alternate contact of holding relay 202. Relay 211 is cut off and released by relay 230 but slow relay 202 is held up over the following circuit: battery, 202. 203, 118, 119, 212, 242, 243, 244, 245, 246, 247, 248, 237 to ground.

The calling line now receives current through relay 249, which operates, operating relay 225. The operation of relay 225 bridges a non-inductive shunt across the winding of 249 and opens the circuit of relay 228 which releases. Holding relay 229, however, is held operated in series with relay 225 at the armature of relay 249. The calling line is now connected directly tothe central office with no bridges of any kind across the circuit. I

When the subscriber hangs up his receiver, relay 249 releases, releasing relay 225. This allows relay 228 to operate and prevent the release of holding relay 229 but the higher resistance of relay 228 permits the supervisory relay at the central office to release and operate the disconnect signal. hen the connection is released at the central office, relay 228 releases, releasing holding relay 229. This releases relays 230 and 202, and when relay 202 releases, it releases relays 219, 117, and 113 and the circuit is ready for another call.

In case of premature disconnect at the central ofiice, relays 249 and 225 release, but

relay 228 does not operate so that after a short interval, relay 229 releases. This releases relay 230, and as the calling subscriber has his receiver off the switch hook, relay 211 operates and prevents the release of relay 202, and operates the line relay at the central oflice to light the calling supervisory lamp.

Tmlc circuitin0oming calls.

When a cord is plugged into the trunk at the central oflice, current supplied through the central office operates relay 228, which in turn operates slow relay 229. The operation of relay 229 lights the busy lamp 210 and operates relay 117 which prevents the trunk from being selected by an originating call. As soon as ringing current is applied-to the trunk, relay 251 operates through its right winding,this circuit including the outer left armature and normal contact of relay 230 rind conductors 233 and 234. Relay 251 in )ttracting its inner left armature locks up to conductor 245 now grounded at the left armature of relay 229 over conductors 246, 247 and 248. The trunk lamp'200, located at the attendants station No. 2 is now lighted over the following circuit: ground, outer left armature and alternate contact of relay 251, 253,200, 254, 123, 100, to battery. Relay 100 operates the buzzer 124 as an audible signal to the attendant. The attendant answers the incoming trunk call by operating the listening key 201, Fig. 2, which connects her telephone set across the line and operates relay 224. The circuit of relay 224 is as follows: battery, 224, 255 256, key 201 to ground. Relay 224 in operating releases relay 251, thus extinguishing the lamp 200, and bridges the holding coil 256 across the trunk in series with the left winding of relay 228. This bridge may be traced as follows: from the upper side of the trunk 226, 257, left winding of 256, 258, 259, right winding of 256, left winding of 228, 260, 233, 252, 234, 235, 236 to the lower trunk conductor 227. The operation of the listening key 201 in opening contact 261 removes a short circuit from the high resistance winding of coil 256. Relay 228 may be shunted out and re leased by the low resistance of the attendants telephone set, but its back contact is connected to its front contact through the right-hand armature and alternate contact of relay 229, and alternate contact 262 of key 201 so that relay 229 remains operated even though relay 228 releases. The guard lamp 291. is in multiple with the winding 224, so that it now lights.

To extend the call to .a station, the attendant operates the dialing key 263, and presses the selecting button (F ig. 1) corresponding to the desired station. The operation of the dialing key operates relay 264 from ground at a contact of the key 201. Relay 264 transfers the attendants telephone set leads to the other side of relay 230, operating relay 211 by a circuit including the attendants telephone set. Relay 264 at its inner left ar mature short circuits the high resistance winding of coil 256 and operates relay 127, this circuit leading from battery 127, 265, 266, 267, 299, 205, 207, 208, to ground at the left armature of holding relay 229.

Relay 211 in operating operates slow holding relay 202 over the following circuit: battery, 202, 203, 113, 119, 212, 213, 453, 527, 512to ground. Relay 127 connects the trunk relays TO to the selecting keys so that the proper one of these relays is operated. As-v suming station No. 1 is called relay 113 is operated to connect the trunk to said station. Relay 113 is operated over a circuit including conductor 115, the innermost left annature of relay 127, key No. 1 to ground. 1 In attracting its inner right armature. it looks up to grounded conductor 136. Ground is also supplied momentarily by the operation of relays 102, 103, through the right arm true and alternate contact of relay 127 to operate relays 268, 269. The circuit of relay 269 includes conductors 2'70, and .271. Relay 268 by its left winding looks through a back contact of the ringing cut-01f relay 272, as follows: battery, star-t relay 505 of the ringing equipment (Fig. 5) .521, 426, 277, 268, 278, 279, 221, 20 5, 207, 20s, to ground "at the left armature of relay 229. Relay 268 connects the called line through the back contactsof relay 269 to the ringing circuit,

but as relay 269 is also operated, ringing current is not applied at this time. The operation of relay 269 connects the sleeve lead 122 '01 :the selected line through the right-hand winding of relay 272 to battery. It the line is busy, this lead is grounded and operates relay 2 2, but ii. the line is idle, relay 272 doesmnot operate and at the end of the vgrroiind impulse from the relays 102, 103, relay .269 releases and connects the line to the ringing circuit and grounds the sleeve lead 122 through the winding of relay 214, this circuit including 120, 217. 216, 218, 215, 214.

Relay 214. operates relay 219 from grounded conductor 221, which relay locks up to said grounded conductor at its right armature, andat its inner left armature, places a direct ground on the sleeve wire 120 to cause the line to test busy. At its right armature it cuts oil relay 127. Interrupted ringing current is now supplied to the called line through the left-hand winding of relay 272, over the following circuit: battery, secondary of transformer 523, 524, 437, 272, 280, 281, 282, 128, 129, through the bell at station No. 1, 130, 1-21, 283, 284, 285, 286, 4.43, 525 to ground.

A portion :of the ringing current passes by way of 287, 288, 289, 290, to the attendants head set as an indication that ringing has been started, the return for the circuit being to ground through the right winding of relay 211.

The attendant now restores the keys 201, 263. Relay 224 remains locked up and keeps 'coil256 bridged across the linein series with low resistance winding of relay 228. Relay 264 releases when key 261 is released, which releases relay 211. Relay 202 releases shortly after the release of relay 211. When relay 202 releases, relay 230 releases and lamp 291 lights.

When the subscriber answers, relay 272 operates, releasing relay 268. The release of relay 268 cuts ringing current off the called lineand connects the called line to relay 211 and releases relay 272. Relay211operates, operating relay 202, and this in turn operates relay 230, and connects the station through to the central office.

Relayl249 thereupon operates, operating relay 225 and .also operating :relay 292 through a make :contact of relay 224. Relay 211 is cut 011' and released by the operation of relay 230, which opens a. circuit of relay 202. Relay 292 locks up and supplies battery to relay 230 independently of relay 202. 'When relay 202 releases, it supplies battery through a contact of relay 225 to operate relay 293. The operation of relay 293 places the locking circuit of relay 224 under .control of relay 249, and also operates relay 20.2 from the left-hand contact of relay 249. Relay 202 in operating cuts off the operating circuit of relay 293, but closes a holding circuit for it vso that relay 293 remains operated as long as relay 202 is operated. Lamp 291 is extinguished by the operation of relays 202-0r 225, as an indication to the attendant that the called subscriber has answered. Relay225 when it operates bridges the noninduc'tive shunt across the winding of relay 249, and removes the short circuit from the high resistance winding of relay 256. Relay 228 may release, but relay 229 is held operated by relay 249.

When the subscriber restores his receiver at the :end of the conversation, relay 249 releases, releasing relays 225 and 224. Relay 228 operates if it has not remained operated during conversation, and prevents the release of relay 229. Upon the release of relay 202, relay .293 releases. The release of relays 224 and 293 opens the bridge across the line through coil 256, leaving the windings of relay 228 in series bridged across the line, and the high resistance winding of relay 228 allows the supervisory relay in the central olfice to release to cause the lighting of the supervisory lamp.

As soon as disconnection takes :place at the central ofiice, relay 228 releases, releasing relay 202. This releases relays 292, 230, 117, and 113 and extinguishes lamp 210, and the circuit is ready for another call.

In case the subscriber wishes to recall the private branch exchange attendant, he clepresses his switch hook momentarily or may operate his calling dial. This releases relay 249 momentarily, unlocking and releasing relay 224. Relay 202, being slow to release, remains operated on the momentary release of relay 249, so that relay 293 remains operated and "the bridge through coil 256 is not opened to-cause the operation ofthe disconnect signal at the called oflice. The release of relay 224 with relay 293 operated connects lamp 200 with the contact of relay 249 so thatthislamp lights as a recall signal.

The attendant .now operates the listening key, which operates relay 224 and extinrguish'es the lamp 200. The attendant may transfer the call to another station by operatingzt-he release key 206. This releases relays 292, 293, 219,113,230, 202, and another line may be selected in exactly the same :manner as or the original selection.

The called subscriber may, in carelessly removing the receiver from the switch hook, close the line circuit and then momentarily open it again. To prevent this from giving releases and operates relay 293. Relay 202 I does not release until an appreciableinterval after relay 211 releases due to the removal of the receiver. Therefore, accidental movement of the receiver hook will not bring in the recall signal because at that time relay 224 is held operated independently of relay 249. In case the line selectedis busy, its sleeve lead 122 is grounded, and when this lead is connected to relay 272 by the operation of relay 269, relay 272 operates, operating relay 2'19, and opening the locking circuit of relay 268. Relay 219 looks up to ground on conductor 221, and at its inner left armature supplies ground through aback contact of relay 214 for holding up relays 269, 268 and 272, and disconnects the sleeve of the called lipe from the right-hand winding of relay 2 2.

Busy tone is connected through condenser 290 to the attendants telephone set. The

attendant may if she desires connect with the' line in spite of the busy test, by operating the no test key 294 and the listening key 201.

This releases relays 268 and 27 2, connecting her telephone set to the called line and removing the busy test. On the release of key 294, relay 268 operates again through its lower winding, but relay 272 does not operate. As relays 269 and 219 are operated and relay 272 is normal, the sleeve of the line is now connected to ground through the winding of relay 214. The relay 214 is short-circuited as long as the line is busy, and, therefore, does not operate. As soon as the line becomes idle, the removal of ground from its sleeve, permits relay 214 to operate, releasing relay 269, and the connection is completed just as if the line had not bcenbusy.

In case the attendant wishes to listen in again on the line before it becomes idle relay 268 will not be released by the operation of key 294, but its back contacts will bebridged by contacts of the key.

In case a call, for any reason, is not extended to a station, the trunk will be held and the lamp 210 will remain steadily lighted until the attendant: releases the trunk by restoring the listening key and operating the disconnect key. This releases relay 224 and opens the bridge across the line, and

permits the supervisory relay at the central office to release. The disconnect key may also .be used for flashing an operator at a manual central oflice or special A position of a machine switching ofiice, by operating the disconnect key with the listening key operated. In this case, the release of the trunk circuit is prevented by the operation of the listening key while the disconnect key opens the line to the central ofiice.

Calls originated by attendant.

lays 224, and 117, and lights lamp 210.

When the call is answered at the central oflice, relay 137 operates, removing ground from the tip. The attendant may extend such a call to a station just as if it were a regular incoming call. In this case, relay 228 will operate, and operate 202 as soon as the dial key is operated.

A call originated in this manner does not require current from the private branch exchange battery, as the relay 224 plays no part in calling the central office, and consequently, no special provision is required for enabling the attendant to call the central office in case of a failure of the power supply at the private branch exchange.

What is claimed is:

1. In a telephone system, subscribers lines, impulse senders therefor, link circuits each having their ends normally connected together. means for connecting a calling line to an idle link, a register comprising a series of counting relays common to said links, means whereby the first impulse from the impulse sender of a calling line causes the association of said register exclusively with theiseized link, relays for connecting called upon the initiation of a call to connect the calling line to said link, a set of relays associable with said link in response to the first impulse from said senders, a relay for connecting the called line with said link under control of the said set of relays, a source of ringing current, means automaticallyv operatedif the called line is idle for connecting said source thereto, and means automatically operated if the called line is busy for preventing the connection of said source thereto. v 3. In a telephone exchange system, telephone lines, senders therefor, a link circuit for interconnecting the same having its ends normally connected together, a relay adapted upon the initiation of a call to connect the calling line to said link, a set of relays associable with said link in response to the first impulse from said senders, a relay for connecting the called line with said link under control of said set of relays, a source of ringing current, means automatically operated if the called line is idle for connecting said source thereto, means automatically operated if the called line is busy for preventing the connection of said source thereto, a source of busy tone current, and means automatically operated if the called line is busy for connecting said latter source to the calling line.

4. In a telephone exchange system, telephone lines, senders therefor, a link circuit for interconnecting the same having its ends normally connected together, a relay adapted upon the initiation of a call to connect the calling line to said link, a set of counting relays associable With said .link in response to the first impulse from said senders, a relay for connecting the called line With said link under control of the counting relays, a source of ringing current, means automatically opera-ted if the called line is idle for connecting said source thereto, and for also producing a ringing tone in the calling line circuit, and means automatically operated if the called line is busy for preventing the connection of said source thereto.

5. In a te ephone exchange system, telephone lines, a sender therefor, a link circuit for interconnecting the same having its ends normally connected together, a relay for connecting said line to said link upon the initiation of a call, a set of counting relays associable with said link in response to the first impulse transmitted by said senders, a relay for connecting the called line to said link under control of said set of counting relays, a source of ringing current, means operated automatically when connection is made with the called line for disconnecting the calling and called ends of said connecting circuit and for connecting said source to the called end, and means operated by the response of the called party for disconnecting said source and reconnecting said calling and called ends.

6. In a telephone system, telephone lines, a link circuit for interconnecting the same having its ends normally connected together, a source of ringing current, a relay operated automatically when connection is made with the called line to disconnect the calling and called ends of said link circuit and to connect said source to the called end, a locking circuit for said relay, and means operated by the response of the called party for opening said locking circuit to release said relay to reconnect said calling and called ends.

7 In a telephone system, telephone lines,

a link circuit for interconnectingthe same, a relay adapted to test the called line and to operate if the line is busy, a source of busy tone adapted to be connected to the calling line by the operation of said relay, means for connecting ringing current to the called line if idle, and a circuit completed through normal contacts of said relay to apply ringing tone to the calling line.

8. In a telephone system, telephone lines, a link circuit for interconnecting the same, a relay adapted to test the called line and to operate if the line is busy, a source of busy tone adapted to be connected to the calling line by the operation of said relay, a source of ringing current, a circuit including serially said ringing source, the called line and said relay closed if the line is idle, said relay being adapted if the line is idle to remain inert and apply ringing tone to the calling line, and to operate upon the response of the called party to cause the opening of said ringing circuit.

9. In a telephone system, telephone lines, a trunk circuit for interconnecting the same, a signaling device for said trunk circuit, a circuit for operating said device as a recall signal, means actuated only after a predetermined interval after the response of the called party for preparing said circuit, and means actuated when the line circuit is thereafter momentarily opened to close said prepared circuit to operate said device.

10. In a telephone system, telephone lines. a trunk circuit for interconnecting the same, a signaling device for said trunk circuit, a

circuit for operating said device as a recall signal, means actuated only after a predetermined interval after the response of the called party for preparing said circuit, means actuated when the line circuit is thereafter momentarily opened to close said prepared circuit, a central office to which said trunk extends, and means actuated when the line circuit is thereafter permanently opened to alter the electrical condition of said trunk.

11. In a telephone system, telephone lines, a link circuit for interconnecting the same, a supervisory relay in said link circuit in circuit with the called line, a signal associated with said link circuit, a circuit for operating said signal, a relay adapted to maintain said circuit open When operated and closed When released, a locking circuit for said relay, means adapted to transfer the control of said locking circuit to said supervisory relay, and a circuit for operating said latter means closed only after a predetermined interval after the called line circuit is closed.

In Witness whereof, I hereunto subscribe my name this 27th day of March A. 1).,

EDWARD E. HINRICHSEN. 

